Global navigation satellite systems (GNSS) provide world-wide signals that principally contain distance information, which allows any user who is receiving such GNSS signals for accurate global localization.
Once the GNSS signal reception is disturbed e.g. through walls inside buildings or much reduced in urban canyons, the required information can no longer be provided to the user and the localization based on pure GNSS fails, or is degraded depending on the amount of information that is still received by the navigation receiver or mobile device.
In order to enhance the accuracy of the position determination satellite based augmentation systems (SBAS) are provided that send messages to the navigation receivers on a second frequency band that is different from the first frequency band on which the GNSS signals are transmitted (L1 band). These SBAS messages comprise accuracy information about the navigation information transmitted on the L1 band from the navigation satellites. The SBAS messages are transmitted from satellites other than the GNSS satellites and from ground stations. Known SBAS systems are the North American WAAS system and the European EGNOS system.
Today's mass-market mobile devices typically already include GNSS receivers or in general GNSS chips, and allow for global localization and navigation accordingly, but face the same signal shadowing or blocking situations once operating in relevant severe environments (e.g. indoor).
This problem of suitable GNSS signal and related information acquisition in severe environments could be avoided by providing GNSS-like signals from locally deployed transmitters, so-called Pseudolites (pseudo-satellites), e.g. installed inside a building to allow for local indoor signal tracking. However, the use of pseudolites installed inside a building is difficult due to signal reflections occurring at the walls and ceilings of the building so that a correct navigation result cannot be achieved.
It is thus a problem to navigate with a GNSS navigation device within buildings or within environments in which reflections of GNSS signals or Pseudolite signals occur.
There are also many needs to contact individuals in a certain area, e.g. in order to transmit a warning message, like hurricane warning or fire alarm, or simply a general information like a commercial advertising.